1. Field of the Invention
The present invention relates to a dry etching method of zinc oxide, and more particularly to a method for manufacturing a zinc oxide semiconductor having improved electrical properties.
2. Description of the Related Art
In general, properties of zinc oxide semiconductors are very similar to those of nitride (GaN) semiconductors. However, the free exciton binding energy of the zinc oxide semiconductors is about 60 meV, which is two-fold larger than that of the nitride semiconductors. The zinc oxide semiconductors have an advantage of growing at low temperature. Accordingly, studies on the zinc oxide semiconductors are actively in progress. As examples of methods for manufacturing zinc oxide thin films, RF and DC magnetron sputtering, laser molecular beam epitaxy, chemical vapor deposition (CVD), pulse laser deposition, etc., can be used. Among these methods, the RF and DC magnetron sputtering enables zinc oxide thin films to grow over broad area at a relatively low temperature, compared to other methods. Accordingly, special attention has been paid to the RF and DC magnetron sputtering.
The zinc oxide semiconductors are currently applied in various optoelectronic devices such as transparent electrodes, sound acoustic wave devices, varistors devices and the like. In order to manufacture these optoelectronic devices using zinc oxide, n-type and p-type zinc oxide thin films of high quality and high concentration are required. Studies on the manufacture of n-type zinc oxide semiconductors have made considerable progress, but p-type zinc oxide semiconductors required for the manufacture of optoelectronic devices have not been successfully manufactured. The optoelectronic devices emit energy corresponding to the respective level differences within the energy band by binding of electrons and holes, in the form of light. Accordingly, without high quality p-type zinc oxide semiconductors, good optoelectronic devices cannot be manufactured.
Conventional methods for manufacturing p-type zinc oxide semiconductors have been reported by many research teams.
For example, Yamamoto et al. suggested that p-type zinc oxide semiconductors can theoretically be manufactured using a codoping method which comprises simultaneously n-type doping using nitrogen (N) as a group IV element and p-type doping using Ga or Al as a group III element [T. Yamamoto et al, Jpn. J. Appl. Phys. Part 2 38, L166 (1999)]. M. Joseph et al. reported a p-type zinc oxide semiconductor having a carrier concentration of 4×1019/cm3 manufactured using Ga and N [M. Joseph et al, Jpn. J. Appl. Phys. Part 2 38, L1205 (1999)]. Since it is reported that the codoping method has a problem of low reproducibility, the codoping method is not recognized to be a stable and reliable method for manufacturing p-type zinc oxide semiconductors.
Another method for manufacturing a p-type zinc oxide semiconductor was reported by T. Aoki et al. This method comprises depositing zinc phosphide (Zn3P2) on a substrate and subsequently heat-treating using a laser [T. Aoki et al, Appl. Phys. Lett. 76, 3257 (2000)]. They also reported that an attempt to prove electrical properties of the p-type zinc oxide semiconductor by Hall measurements was not successful. Accordingly, the method of T. Aoki et al. has disadvantageous in terms of poor electrical properties and inefficient manufacturing processes.
Y. R. Ryu et al. reported a method for manufacturing p-type zinc oxide doped with arsenic (As) [Y. R. Ryu et al, J. Crystal Growth 216, 330 (2000)]. However, the p-type electrical properties seem to be exhibited due to a new interfacial layer formed through an interfacial reaction between a GaAs substrate and a zinc oxide thin film, rather than the manufactured p-type zinc oxide. Accordingly, this method is not yet widely recognized.
Recently, many research teams reported successful manufacture of p-type zinc oxide semiconductors doped with nitrogen (N) recognized as an optimal dopant [For example, D. C. Look et al, Appl. Phys. Lett. 81, 1830 (2002)]. In the method of D. C. Look et al., however, the manufactured p-type zinc oxide semiconductor is changed to an n-type zinc oxide semiconductor with the lapse of time. Accordingly, the method has a disadvantage of poor stability.
As discussed above, p-type zinc oxide semiconductors having excellent reproducibility and reliability are not successfully manufactured.